Alternate Signaling Mechanism Using Clock and Data

ABSTRACT

Control events may be signaled to a target system having a plurality of components coupled to a scan path by using the clock and data signals of the scan path. While the clock signal is held a high logic level, two or more edge transitions are detected on the data signal. The number of edge transitions on the data signal is counted while the clock signal is held at the high logic state. A control event is determined based on the counted number of edge transitions on the data signal after the clock signal transitions to the low logic state.

CLAIM OF PRIORITY

The present application claims priority to and incorporates by referenceU.S. Provisional Application No. 61/084,474 filed Jul. 29, 2008,entitled “Topology Discovery Training.” The present application alsoclaims priority to and incorporates by reference U.S. ProvisionalApplication No. 61/084,471 filed Jul. 29, 2008, entitled “SeriesEquivalent Scans Across Multiple Scan Topologies.” The presentapplication also claims priority to and incorporates by reference U.S.Provisional Application No. 61/084,463 filed Jul. 29, 2008, entitled“Selecting a Scan Topology.” The present application also claimspriority to and incorporates by reference U.S. Provisional ApplicationNo. 61/084,458 filed Jul. 29, 2008, entitled “Automatic Scan FormatSelection Based on Scan Topology Selection.” The present applicationalso claims priority to and incorporates by reference U.S. ProvisionalApplication No. 61/084,453 filed Jul. 29, 2008, entitled “DynamicBroadcast of Configuration Loads Supporting Multiple Transfer Formats.”The present application also claims priority to and incorporates byreference U.S. Provisional Application No. 61/084,439 filed Jul. 29,2008, entitled “Timing Protected Detection of Alternate SignalingMechanism Using Clock and Data.”

FIELD OF THE INVENTION

This invention generally relates to the field of testing integratedcircuits and systems containing integrated circuits.

BACKGROUND OF THE INVENTION

The IEEE 1149.1 standard was adopted in 1990. Built upon the work of theJoint Test Action Group (JTAG), it provided a pins-out view from one ICpad to another to help test engineers locate and discover faulty PCboards. A description of the boundary scan description language wasadded in 1994.

Complications arose as chips increased functionality and designs shiftedaway from PC boards to multichip modules and stacked die packages. Thesedifficulties included handling the pin count requirements and multipleTest Access Port (TAP) controllers for System-on-Chip (SoC) devices,testing multichip modules and stacked die configurations, enhancingdebug performance, and improving test and debug logic power-down inlow-power conditions.

Organizations like the Mobile Industry Processor Interface Alliance andthe NEXUS 5001 Forum took up the challenge to solve the problemsspecific to their industries.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is a block diagram illustrating a target system with series scantopology;

FIG. 2 is a block diagram illustrating a target system with four-wirestar scan topology;

FIG. 3 is a block diagram illustrating a target system with two-wirestar scan topology;

FIG. 4 is a block diagram of a target system with mixed use oftechnologies and scan topologies;

FIG. 5 is an illustration contrasting 1149.1 and 1149.7 test views;

FIG. 6 is a series topology with mix of TAP.7s plus TAP.1s or TAP.7swith no TSL;

FIG. 7 is a block diagram illustrating TAP.7 TAPC hierarchy;

FIG. 8 is an illustrative block diagram of system connectivity supportedby TAP.7 architecture;

FIGS. 9A-9D illustrate signaling of commands using the TCK(C) and TMS(C)signal lines;

FIGS. 10A and 10B are timing diagrams illustrating variation in edgedetection due to propagation delay;

FIG. 11 is a conceptual schematic of the control event detectionfunction; and

FIG. 12 is a flow diagram event signaling in a target system.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As chips add new functionality and system designs evolve away fromboards and toward multi-chip system-on-chip (SoC) architectures,developers of handheld and consumer electronics are faced with stricterpin and package constraints. The IEEE 1149.7 standard is a new two-pintest and debug interface standard that supports half the number of pinsof the IEEE 1149.1 technology, allowing developers to easily test anddebug products with complex digital circuitry, multiple CPUs andapplications software in products such as mobile and handheldcommunication devices.

Systems and integrated circuits that utilize IEEE 1149.7 may be designedto include a complex scan topology. Circuits and methods for determiningcontrol events signaled on the clock and data line of a two-wire orfour-wire interface will be described in more detail below.

The IEEE 1149.7 is a complementary superset of the widely adopted IEEE1149.1 (JTAG) standard that has been in use for more than two decades.This standard defines a port into embedded systems for devicemanufacturing, testing and software development during systemdevelopment. In addition to maintaining compatibility with IEEE 1149.1,the new standard improves debug capabilities and reduces SoC pin-countrequirements. It also standardizes power-saving conditions, simplifiesmanufacturing of multi-chip modules and stacked die devices, andprovides the ability to transport instrumentation data. Concepts andterminology used in IEEE 1149.1 and in IEEE 1149.7 are used in a similarmanner herein and are therefore not described in detail herein.

Rather than replacing IEEE 1149.1, the new IEEE 1149.7 standard expandsits functionality while reducing the number of pins used in someconfigurations. It supports new scan topologies that are favorable tostacked die and multichip module configurations and offers advancedcapabilities to aid in software debug. It describes circuitry that maybe added to an integrated circuit to provide access to on-chip IEEEstandard test access ports (TAPs) specified by IEEE Std 1149.1-2001. Itprovides complete backward compatibility with the 1149.1 standard whileaggressively adding features to supporting applications test and debug.The circuitry uses IEEE Standard 1149.1-2001 as its foundation.

The 1149.7 Standard delivers these capabilities with six classes of testaccess ports (T0-T5), with each class providing incremental capability.The IEEE 1149.7 standard has two groups of capabilities: Classes T0through T3, which extend IEEE 1149.1 and enable new operations using theIEEE 1149.1 protocol, and Classes T4 and T5, which are focused onadvanced two-pin operation using an Advanced Protocol.

Class T0 ensures compliance with the industry's test infrastructure bysetting up IEEE 1149.7 devices to make them act compatibly with IEEE1149.1. These techniques include the use of N-bit IR, 1-bit DR forbypass instruction, mandatory IDCODE (32-bit path), and mandatoryinstructions behaving as specified in the IEEE 1149.1 specification.After a test logic reset is initiated, all multi-TAP devices mustconform to the mandatory IEEE 1149.1 instruction behavior and implementa 1-bit DR scan for the bypass instruction. FIG. 1 illustrates such asystem. Debug test system (DTS) 100 is generally a computer based systemthat provides control and a user interface for testing an integratedchip, printed circuit board or SoC using IEEE 1149.1 that has beenenhanced to support the IEEE 1149.7 protocols. DTS 100 may be an XDSemulator from Texas Instruments, for example. Modules 110(1)-110(n) arerepresentative of various modules that may be interconnected to DTS 100using various aspects that will be described in more detail below.

Class T1 instantiates a control system for the IEEE 1149.7 standard thatis transparent to IEEE 1149.1 devices, providing a foundation for theadvanced functionality implemented in Classes T1 through T5 withoutchanging the IEEE 1149.1 state machine. It supports standardized testand functional resets along with power management of the TAP controllerand test logic.

Class T2 offers a chip-level bypass mechanism that shortens scan pathsand another mechanism that provides hot connect capability to achievehigher performance for testing high chip count applications.

Class T3 provides for boundary scan testing using a four signal startopology (Star-4), with TAP selection built into the TAP.7 controller,unlike the use of a Star-4 Scan Topology described by the IEEE 1149.1Standard. A T3 TAP may be deployed in either a series or star scantopology. A star topology is preferable for testing stacked dieconfigurations. Whereas FIG. 1 shows the series scan topology, FIG. 2illustrates the Star-4 or Wide Star configuration. In this case, modules210(1)-210(n) are connected in a parallel manner using four wires andmay be connected to DTS 200 that is configured to provide control over astar connected system, as will be described in more detail below. Directaddressability is included with T3 and above TAP.7 controllers.

Class T4 provides a reduction of number of test and debug pins in SoCdevices, It supports scan transactions with two pins instead of four,resulting in fewer total pins required on chip packages. This also helpswith stacked die configurations because it is highly desirable to havedebug pins connected in parallel when dies are stacked. Two-pinoperation is provided by eliminating the original data lines and sendingbidirectional serialized data over the Test Mode Select (TMS) line,which is renamed TMS Counter (TMSC). To implement this capability, theglueless star configuration from Class T3 is utilized, this time withoutTest Data In (TDI) and Test Data Out (TDO). This is the Star-2configuration shown in FIG. 3 in which an illustrative SoC 300 includesseveral die 302(1)-302(n) connected in a Star-2 arrangement using onlytwo wires in a parallel manner. Of course, other embodiments may havefewer or more die and still use the two pin interconnection. Otherembodiments may use the two pin interconnect for interconnection ofpackaged chips as well as bare or stacked die.

To address the rising number of pins in SoC devices, Class T4 adds scanformats to support transactions with two pins instead of four, resultingin fewer total pins required on chip packages. This also helps withstacked die configurations because it is highly desirable to have thefewest number of connectors possible when die are stacked. The key totwo-pin operation is eliminating the original data lines and sendingbidirectional serialized data over the Test Mode Select (TMS) line,which is renamed TMS Counter (TMSC). To implement this capability, theglueless star configuration from Class T3 is utilized, this time withoutTest Data In (TDI) and Test Data Out (TDO). This is the Star-2configuration shown in FIG. 3 in which an illustrative SoC 300 includesseveral die 302(1)-302(n) connected in a Star-2 arrangement using onlytwo wires in a parallel manner. Of course, other embodiments may havefewer or more die and still use the two pin interconnection. Otherembodiments may use the two pin interconnect for interconnection ofpackaged chips as well as bare or stacked die.

Besides reducing pin count, Class T4 defines optimized download-specificscan modes in which only useful information is downloaded. To improvepin operation performance, the clock rate also can be doubled. Thesefeatures combined with the optimized transactions do not causeperformance loss, instead improving performance in some cases.

Class T5 functionality is beneficial primarily to software designersutilizing a Test Access Port for debugging. This class gives the testport the ability to perform debug and instrumentation operationsconcurrently (data is transferred during idle time), which reduces thenumber of pins dedicated to instrumentation, and enables customprotocols to use the pins, a feature many vendors offer in nonstandardways. Class T5 standardizes the process to access the pins. Class T5provides both scan and data transport transactions using the two wireinterface.

FIG. 3 also illustrates a debug test system (DTS) 310 coupled to SoC300. DTS 310 is generally a computer based system that provides controland a user interface for testing an integrated chip, printed circuitboard or SoC using IEEE 1147.1 that has been enhanced to support theIEEE 1147 protocols and two-wire interface, as will be described in moredetail below. DTS 310 may be an XDS emulator from Texas Instruments, forexample.

T0-T3, and T4/T5 four pin TAP.7s may be deployed in a Series Scantopology. T3 and T4/T5 four pin TAP.7s may be deployed in a Star-4 Scantopology. T4-T5 TAP.7s may be deployed in a Star-2 Scan Topology. Whendeployed in these scan topologies, all classes can traverse the statediagram using a common protocol (Standard—the legacy IEEE 1149.1protocol). In the Series Scan Topologies data transfers to conventional1149.1 instruction and data registers are performed with the StandardProtocol. In the Star-4 scan topology data transfers are performed withthe Standard Protocol modified to prevent drive conflicts, with theability to select the scan paths of only one TAP.7 controller in thetopology at a time. This provides for sequential access to the paths ofeach TAP.7 controller in the branch. In the Star-2 scan topology, datatransfers are performed only with the Advanced Protocol. The selectionmechanisms for scan paths and TAPCs available with Star-4 operation arealso available with Star-2 operation. Classes T0-T2 allow the use onlythe Standard Protocol, Class T3 allows the use of the Standard Protocolto traverse the TAPC state diagram and a modified Standard Protocol toeither traverse the state diagram or perform data transfers in theShift-IR and Shift-DR states. Classes T4 and T5 allow the use of theStandard Protocol to traverse the TAPC state diagram, a modifiedStandard Protocol to either traverse the state diagram or perform datatransfers in the Shift-IR and Shift-DR states, when operated in a Star-4Scan Topology, and Advanced Protocols to either traverse the statediagram or perform data transfers in the Shift-IR and Shift-DR stateswhen operated in a Star-2 Scan Topology. It is important to note thatwith deployment in Star-4 and Star-2 topologies, TAP.7 controllersperform data transfers in these scan topologies using protocols uniqueto the topology in which they are deployed.

The operation of each of these Scan Topology Branches supports theselection of individual TAPCs and the scan paths associated with themduring their independent operation. This is covered in the 1149.7standard and not in this description.

TAP.7 architecture provides for the operation of Series, Star-4, andStar-2, Scan Topologies and other technologies sharing the TCK(C),TMS(C), TDI(C), and TDO(C) connections to a Debug Test System directingscan activity. These Scan Topologies are called branches of the systemscan topology. With this architecture, an Adapter Test Access PortController (ADTAPC) is the gateway to scan facilities of a chipimplementing an 1149.7 Test Access Port. The ADTAPC controls access to aChip-Level Test Access Port Controller (CLTAPC) that provides access tochip-level scan paths

Since a typical boundary scan operation requires scanning theinstruction registers and boundary scan cells of one or more devicesbetween the Select-xR and Update-xR states, a method is needed toduplicate the scan transaction available with a Series Scan topologywhen more than one scan topology is involved. With this description,states such as the Capture-xR and Update-xR TAP are to be interpreted asfollows: the “x” refers to either “D” for data or “I” for instruction.Embodiments of the invention may provide this equivalent function, aseries equivalent scan.

Series equivalent scans of a complex scan topology, i.e., a scantopology with two or more branches in which at least two of the branchesare of differing technologies (see Table 1), sharing the same controland data signaling create the equivalent of an 1149.1 series scan thatbegins with the Select-xR state and ends with the Update-xR state. Witha series Scan Topology, all scan paths of interest are scanned at thesame time between these states. With a complex scan topology, this isnot possible as methods used to transfer data to and from scan pathspresented by Series, Star-2, and Star-4 Scan Topologies and othertechnologies is different.

With series equivalent scans, a scan is broken into sections consistingof one or more scan sections. With an 1149.7 Test Access Port, the scansection is one or more sequences of the Exit2-xR, one or more Shift-xRstates, Exit1-xR, and one or more Pause-xR states). With anothertechnology, scan data would be delivered as defined by the technology.These scan sections are sandwiched between a preamble (Select-xR,Capture-xR, Exit1-xR, and one or more Pause-DR states) and a postamble(Exit2-xR and Update-DR states). A single branch is selected between thepreamble and the first scan section and between scan sections. Allbranches are selected between the last scan section and the postamble.With the sequence described above, all or some CLTAPCs in all branchesprogress from either the Test-Logic-Reset or Pause-xR state to thePause-xR state without encountering an Shift-xR state. The TAPCs of allbranches of interest operate in lockstep during the preamble andpostamble state sequences, with only the TAPCs within branches that areselected during scan sections.

TABLE 1 Protocol usage by Technology TAPC Topology Operation of BranchesState Protocol Selected Series Star-4 Star-2 Other Select-xR StandardAll Active Active Active Active Capture-xR Standard All Active ActiveActive Active Exit1-xR Standard All Active Active Active Active Pause-xRStandard All Active Active Active Active — — — Select-Series. Pause-xRStandard Series Active Dormant Dormant Dormant Exit2-xR Standard SeriesActive Dormant Dormant Dormant Shift-xR Standard Series Active DormantDormant Dormant — — — Shift-xR Standard Series Active Dormant DormantDormant Exit1-xR Standard Series Active Dormant Dormant Dormant Pause-xRStandard Series Active Dormant Dormant Dormant — — — Select-Star-2Pause-xR Advanced Star-2 Dormant Dormant Active Dormant Exit2-xRAdvanced Star-2 Dormant Dormant Active Dormant Shift-xR Advanced Star-2Dormant Dormant Active Dormant — Shift-xR Advanced Star-2 DormantDormant Active Dormant Exit1-xR Advanced Star-2 Dormant Dormant ActiveDormant Pause-xR Advanced Star-2 Dormant Dormant Active Dormant — — —Select-Star-4 Pause-xR Modified Std Star-4 Dormant Active DormantDormant Exit2-xR Modified Std Star-4 Dormant Active Dormant DormantShift-xR Modified Std Star-4 Dormant Active Dormant Dormant — Shift-xRModified Std Star-4 Dormant Active Dormant Dormant Exit1-xR Modified StdStar-4 Dormant Active Dormant Dormant Pause-xR Modified Std Star-4Dormant Active Dormant Dormant — — — Select-Other Pause-xR Tech. DefinedOther Dormant Dormant Dormant Active Exit2-xR Tech. Defined OtherDormant Dormant Dormant Active Shift-xR Tech. Defined Other DormantDormant Dormant Active — Shift-xR Tech. Defined Other Dormant DormantDormant Active Exit1-xR Tech. Defined Other Dormant Dormant DormantActive Pause-xR Tech. Defined Other Dormant Dormant Dormant Active — — —Select-All Pause-xR Standard All Active Active Active Active Exit2-xRStandard All Active Active Active Active Update-xR Standard All ActiveActive Active Active

Table 1 lists various protocols that may be used with a SeriesEquivalent Scan. A protocol understood by the TAPCs of a selected branchis used to drive the state progression of a scan section. It is notnecessary that the TAPCs forming a deselected branch understand theprotocol used during this state progression. Scan operations areperformed on the selected branch while the other branches remaindormant. Branches that are not selected remain dormant and ignore theprotocol being used until they are selected. Once all branches areselected following the last scan section, the TAP controllers formingall branches move through the Update-xR and Capture-xR states in lockstep. This provides the function of a series scan.

In summary, a scan of the paths with a branch move the state of theTAPCs forming the branch to Pause-xR, sequentially selecting andscanning the scan paths of interest within each branch beginning andending the scans in the Pause-xR state. Once these scans are complete,the update/capture operation is performed simultaneously in all TAPCs ofall branches of interest The TAPC state may be moved from the Update-xRstate to either the Run-Test/Idle state or Select-DR state on to thePause-xR state where the sequential scans can again be performed. Thisprocess preserves the timing between the Update-xR and Capture-DR stateswhen portion of the operation that does not include the Shift-xR stateis performed using the Standard Protocol.

The Run-Test-Idle state may also be used to select branches. Thiscapability can be used to select a branch and park the state of one ormore of the TAPCs forming the branch. This may be sequentially done forall branches. Only those TAPCs within a branch that are not parked mayleave the Run-Test-Idle state. When all branches are selected and theTAPC state moved to the Pause-DR state via the Select-DR state. TheTAPCs whose state is parked in Run-Test-Idle state do not participate inthe scans.

A Selection Escape Sequence is used to initiate a selection sequence.This sequence can select all ADTAPCs within a branch while deselectionall ADTAPCs within other branches or select all ADTAPCs within allbranches. A deselection escape sequence deselects all ADTAPCs of allbranches. Although selection and deselection escapes can be associatedwith any ADTAPC state, they are expected to be used while in thePause-xR and Run-Test-Idle states. This process will be described inmore detail below.

DTS/TS Connectivity

The TAP.7 architecture supports both simple and complex systemconnectivity with a graduated set of capability. A system may deploy anymix of TAP.1s, TAP.7s, and potentially other legacy technologies asshown in FIG. 4, which is a block diagram of a target system with mixeduse of technologies and scan topologies.

Most systems will implement only one branch of the connectivity shown inthis figure. In most cases, the target system (TS) will only have alimited number of TAPs. Other architectures, represented by branches406, 407, can also be included as additional branches that are separatefrom those shown in FIG. 4 in a custom scan topology. These branches arecontrolled in manner similar to TAP.7 branches.

Technology Branches

FIG. 4 is the union of simpler types of connectivity called technologybranches. Each of the branches 402-407 shown in this figure may beoperated separately for debug purposes. They may also be operated in amanner that provides Series Scan Equivalency across the branchescontrolled with the TCK1 and TCK(C) signals. Proprietary technologiesare generally operated separately but may be operated with TAP.7controllers in as shown in Table 1.

Other embodiments may have various combinations of branch operation.Other embodiments may use different sets of commands, protocols, events,etc. The list of protocols in Table 1 is not intended to be limiting toembodiments of the invention in any manner.

The TAP.7 branches 403-405 have one or more TAP.7s connected in Series,Star-4, and Star-2 Scan Topologies. These branches contain logic toselect or deselect an ADTAPC, indicated generally at 410. This logicprovides for the selection and deselection of these branches withSelection and Deselection Escape Sequences. ADTAPC selection logic isoptional for T0-T2 TAP.7s and mandatory for T3 and above TAP.7s.Including this logic in T0-T2 TAP.7s supports their deployment insystems where T4(N) and T5(N) TAP.7s may be deployed.

The TAP.1 branch 402 includes a TAP.1 or a T0-T2 TAP.7 withouttechnology selection logic connected in series with other TAP.1s orTAP.7s. It operates with the standard protocol and TAPs with the four1149.1 signals. This branch is selected using the TCK1 signal shown inthis figure as it has no built-in selection mechanism. T0-T2 TAP.7swithout selection are included in a branch that is this type. The ADTAPCselection logic may be added to the current 1149.1 technology to make itselectable using common connectivity.

Proprietary technologies 406, 407 may be connected in parallel with theTAP.7 branches provided: the technology has a dedicated clock and atleast one control/data input; the technology implements the technologyselection mechanisms and protocols defined by the 1149.7 standard; andthe clock pin of the technology is connected to the TCK(C) signal andthe control/data pin is connected to the TMS(C) signal.

As noted previously, a TAP.1 branch is selected by keeping its TCK orTMS signal separated from the signal of like name of branches and gatingone of the separate signals to deselect the branch. The gating of theTCK signal of this type of branch is used to select these types ofbranches. In some embodiments, TAP.1s and T0-T2 TAP.7s without theTechnology Selection Logic (TSL) are selected using in this manner. Insome embodiments, any branch may be selected in this manner if desired.

TAP.1s and TAP.7s can be deployed in topology branches as shown in Table2. Each of these topologies is considered a technology within thisdocument.

TABLE 2 Branch/technology deployment permissibility T0-T2 w/o w/ BranchProprietary TAP.1 TSL TSL T3 T4 (W) T5 (W) T4 (N) T5 (N) TAP.1 No YesYes Yes Yes Yes Yes No No Series TAP.7 No No No Yes Yes Yes Yes No NoSeries TAP.7 No No No No Yes Yes Yes No No Star-4 TAP.7 No No No No NoYes Yes Yes Yes Star-2 Proprietary Yes No No No No No No No No

Chips, Components, and Boards

With the TAP.7 architecture, any part of this connectivity shown in FIG.4 may be deployed on a board, within a package, or within a chip. Thiscomprehends the packaging and integration trends since the inception ofthe 1149.1 Standard.

The IEEE 1149.1 test view allows only one TAPC per component. The 1149.7test view is a superset that allows multiple TAPCs per component. Withthe 1149.7 test view, a component: is either a package containing one ormore chips, or a direct mount chip; provides access to one or more TAP.1or TAP.7 controllers through the same or separate pins; and providesaccess to proprietary TAPCs or other technologies through the same orseparate pins. This superset blurs the boundary between board,component, and chip. This blurring allows operation across thoseboundaries as shown in FIG. 5. When there is only one TAPC percomponent, the 1149.1 and 1149.7 test views are described by boundaryscan description language (BSDL). When there is more than one TAPC percomponent the 1149.7 test view requires hierarchical scan descriptionlanguage (HSDL), plus BSDL for each endpoint.

TAP.7 Deployment Scenarios

Series branches may be constructed from TAP.1s and four pin TAP.7s asshown in FIG. 6. This scan topology may share the TMS, TDI, and TDOconnectivity with another topology provided TCK(C) or TMS(C) signal isused to select/deselect this topology.

In most cases, one or more TAP.7s is connected in one of the ScanTopologies shown in FIGS. 1-3. Note that the convention for naming DTSTDI/TDIC and DTS TDO/TDO signals in FIGS. 1-3 is: 1) The DTS TDI/TDICsignal sources chip TDI information; 2) The DTS TDO/TDOC signal is thedestination for chip TDO information.

The Star-2 Scan Topology illustrated in FIG. 3 is a subset of both theSeries and Star-4 Scan Topologies. This means that the Series and WideStar Scan Topologies may be operated as a Star-2 Scan Topology whenevery test access port sharing the connection is a T4 and above TAP.7.

Chip TAPC Hierarchy

A hierarchical view of TAPCs within a chip is needed to maintain IEEE1149.1 compliance and provide solutions to the compatibilityrequirements identified earlier. For a given chip, three or more levelsof TAPC hierarchy are accommodated as follows:

1^(st) level—a TAPC within the TAP.7 controller—the primary interface tothe DTS.

2^(nd) level—a TAPC at the chip-level (CLTAPC).

3^(rd) level—embedded TAPCs connected to the chip-level TAPC.

Other levels, if needed.

While all levels of the TAPC hierarchy need not be present in all chips,the TAP.7 architecture accommodates them when they occur. The TAPChierarchy is shown in FIG. 7. Exemplary chip 700 includes TAPC 702 thatis implemented as a T0 with control events or a TSL for T1 and above.Chip level TAPC (CLTAPC) 704 operates under Adapter TAPC (ADTAPC) 700.Embedded TAPC(s) (EMTAPCs) 705 operate under CLTAPC 704. Additionallevels of EMTAPCs 706 may be embodied as needed. The EMTAPC(s) 705 andEMTAPC(s) 706 are hidden following a test reset.

A chip with IEEE 1149.7-compliant behavior always has a Chip-Level TAPC702. It may also include one or more Embedded TAPCs 704, all of whichare considered subordinate to the chip-level TAPC (CLTAPC). The CLTAPCis considered the parent of the Embedded TAPC(s). The addition of theEnhanced Protocol Unit (EPU) to a T1 or above TAP.7 controller adds theADTAPC but does not add instruction or data registers in series orparallel with those associated with the CLTAPC and the EMTAPCs. TheADTAPC is considered the parent of the CLTAPC. The addition of theAdvanced Protocol Unit (APU) in a T4 or T5 TAP.7 does not add anadditional TAPC or level of TAP.7 TAPC hierarchy.

The ADTAPC 702 is connected to the CLTAPC 704. The CLTAPC may provideaccess to EMTAPCs. The EMTAPCs are hidden following a Test Reset topresent the test view of a component specified by the 1149.1 Standard.The “other TAPCs” portion of the hierarchy can have additional levels ofhierarchy. The TAPC hierarchy may vary dramatically by chip, with theTAPs accessed varying by application. In one or more embodiments of theinvention, the DTS dynamically manages the TAPC hierarchy to:accommodate a Star Scan Topology, minimize the length of the scan path,and avoid non-functional parts of the hierarchy.

Combined View of TAP Connectivity and TAPC Hierarchy

The combination of the system shown in FIG. 4 and the TAP.7 TAPhierarchy shown in FIG. 7 creates the system connectivity and TAPChierarchy shown in FIG. 8. The selection layers (labeled A-E) are shownthis figure. The entities actually selected and deselected are shown atthe bottom of this figure.

Selection Concepts

Additional selection concepts beyond those supported by the IEEE 1149.1standard are provided to access to the CLTAPCs and EMTAPCs shown in FIG.8. These concepts support the use of the selection hierarchy, theparking of CLTAPC and EMTAPC states and resynchronization of the CLTAPCand EMTAPC to the state of their parent, and common signaling acrosstechnologies.

Hierarchical Selection and Deselection TAPCs

These concepts provide the DTS the means to interact with all or asubset of the technology connected to it. They provide a means to selectthe various levels of the hierarchy shown in FIG. 8. Lower levels of thehierarchy become usable when all nodes above it are selected and becomeunusable when any node above it is deselected. Selection and deselectionis provided at the following nodes in the hierarchy: specifictechnology, Series, Star-4, Star-2, or all TAP.7 Scan Topologies, anADTAPC within a TAP.7 Scan Topology (depending on the ADTAPC state), aCLTAPC connected to an ADTAPC, and EMTAPCs connected to a CLTAPC.

A command sequence is provided to establish the scan topology in which aTAP.7 TAPC is deployed since the TAP.7 controller needs to know the scantopology in which it is deployed. Selection/deselection interoperabilitywith proprietary, legacy, and TAP.7 technologies is provided through theuse of a common set of signaling conventions for these functions. TheDTS and TS exchange information in one of two ways: 1) A TCK(C) signaledge sampling the TMS(C) signal value; and 2) a count of TMS(C) signaledges while the TCK(C) signal is a logic 1. Both of these means may beused concurrently within the same TCK(C) bit period. The followingsignaling characteristics make this possible.

Control events to perform selection and de-selection are sent from theDTS to the scan topology via the TCK(C) and TMS(C) signal lines andreceived by the various TAPCs included within the topology. A TAP.7 TAPCinterprets the count of the number of TMS(C) edges while TCK(C) is alogic 1 as one of four control events. Each control event has adifferent function and TMS(C) edge count. These control events, theiredge count, and their function are described below and shown in FIGS.9A-9D. Table 3 lists the four control events.

TABLE 3 Control Events signaled via TCK(C) and TMS(C) Custom (2 or 3edges) Performs a technology specific function. Deselection (4 or 5edges) Initiates the deselection of an online technology. Selection (6or 7 edges) Initiates the selection of a technology via a subsequentselection test Reset (>7 edges) Resets all technologies (generates aType-3 TAP.7 TAPC reset)

The DTS creates a control event by generating one or more TMS(C) edgepairs while the TCK(C) signal is a logic 1 value as shown in FIGS.9A-9D. Even and odd TMS(C) edge counts beginning with two are given thesame meaning. This accommodates the case where a change of state of theTMS(C) signal related to data occurs while the TCK(C) is a logic 1. Thiscan occur because of propagation delays when a change in state of theTMS(C) signal is initiated by a falling edge of TCK(C) or by a change instate of the TMS(C) signal is initiated by a rising edge of TCK(C).

This approach allows the interoperability of technologies that changetheir data/control signal with the different edges of the clock. Therelationship between the TAP.7 class and the deployment of control eventdetection is shown in Table 4.

TABLE 4 TAP.7 class/control event deployment relationships ClassCapability T0-T1 T2 T3 T4 and above Control Event Optional OptionalMandatory Mandatory Detection

The implementation of Control Event Detection becomes mandatory forT0-T3 TAP.7s when the optional TAP.7 Selection Logic is implemented withthese TAP.7 classes. Their detection and use may be easily added as awrapper to TAP.1 and many other technologies without changing theunderlying technology in any way.

Since the TMS(C) signal is used as a clock with control events, careshould be taken to minimize board-level transmission line effects toassure their proper operation.

In some embodiments, a control event is detected only when a reset isnot asserted to the detection circuit. It begins and ends while theTCK(C) is a logic 1 and uses TMS(C) as a clock while the TCK(C) is alogic 1. In this manner, additional control information is overlaid ontothe information that is normally transferred with the TCK(C) and TMS(C)without changing the information. Control events are detected whenTCK(C) is a logic 1 regardless of the TCK(C) and TMS(C) drive histories.

The detection of the four control events is shown in FIGS. 9A-9D. FIG.9A illustrates a custom event. An online technology can use the customevent in any manner it chooses. It is not used with T0-T3 TAP.7s. It isused as an End of Transmission (EOT) event with T4 and above TAP.7s.FIG. 9B illustrates selection events while FIG. 9C illustratesdeselection events. FIG. 9D illustrates a Reset Event. A reset eventinitializes all technologies sharing the TCK(C) and TMS(C) connectivity.A reset event resets the technology. It is recommended that this resetoccur with the falling edge of TCKC other than inhibiting the drive ofthe TMS(C) pin. With a TAP.7 controller, it generates a Type-3 reset.This event generates a Type-3 reset beginning with falling edge ofTCK(C) following the asynchronous detection of the event.

The TAP.7 controller logic may accommodate the possibility that theTMS(C) edge establishing the TMS(C) value for the bit period may occurafter the TCKC signal is a logic 1. Changes in data values occurrelative to the falling edge of the test clock but may appear at the TSinputs after the rising edge of the test clock as a result of analogdelays in the system. This means the TAP.7 controller should interpretan odd number of edges occurring while TCK(C) is a logic one as the nextlowest even number. This makes the TAP.7 controller's escape sequencedetection logic insensitive to the timing relationship of the TCK(C)falling edge and a change in the TMS(C) value generated by the TCK(C)falling edge.

DTS Responsibilities

The DTS should assure the TMS(C) signal logic level at the beginning andend of the bit period coincident with a control event is the valuerequired to convey the TMS(C) value for the bit period. The DTS shouldseparate the first TMS(C) edge associated with a control event from thepreceding TCK(C) falling edge and other TMS(C) edges associated with acontrol event by at least one minimum TCK(C) period, and separate thelast TMS(C) edge associated with a control event and the subsequentTCK(C) falling edge by at least one minimum TCK(C) period. Timingconsiderations of interface power-down modes should be considered whensetting the duration of the TCK(C) logic 1 time for control eventgeneration.

In some embodiments, since the TCK(C) pin must be a logic 1 while TMS(C)is toggled, it is generally only practical to generate escape sequenceswhen the DTS sources TCK(C). The n and n+1 nature of escape sequencesaccommodates designs where, at the highest TCK(C) frequency, there is apossibility that data transitions on the TMS(C) pin initiated by thefalling edge of the TCK(C) may be delayed sufficiently (e.g., by apropagation delay) so as to occur following the rising edge of theTCK(C). In this case this edge is counted in addition to the even numberof edges of TMS(C) creating an escape sequence, creating an odd TMS(C)edge count as described previously.

FIGS. 10A and 10B are timing diagrams illustrating variation in edgedetection due to propagation delay. FIG. 10A illustrates the case wherethe transition of the last data edge 1002 on the TMS(C) line occursprior to the clock signal being held high as indicated at 1004. FIG. 10Billustrates the case were the transition of the last data edge 1006occurs after the clock signal being held high as indicated at 1004. Inthis case, the delayed transition may be included in the edge count. Inorder to avoid confusion, an extra edge is accommodated in the edgecount analysis, as discussed above.

Example Circuit for Control Event Detection

An example of a circuit that may be used for event detection is shown inFIG. 11. This circuit is to be viewed as only an example of how eventdetection may be accomplished. Other methods of event detection may beused. The control event detection logic shown in this figure operates asfollows: Certain TAP.7 controller resets (Type-0-Type2) initialize thislogic; at start-up, the default TCK(C) signal value is a logic 1; thebehavior of the TMS(C) signal is determined by the TAP.7 controllerstart-up option; CE_CLEAR is asserted by a falling edge of TCK(C) andreleased by a rising edge of TCK(C); it is released by Type-0, Type-1,and Type-0 resets when these resets initialize this function.

After CE_CLEAR is deasserted, a rising edge of CE_CLOCK causes thecounter to increment thermometer code counter 1110. The CE_CLOCK iscreated with the XNOR of the TMS(C) signal and the last value TMS(C)value sampled with the falling edge of TCK(C). This assures the firstedge created by a normal change in TMSC data creates a falling edge ofthe CE_CLOCK signal. This edge is therefore discarded by the thermometercode counter 1110 that counts TMS(C) edges when it occurs after CE_CLEARis released. When an even number of edges is created, there will be nCE_CLOCK rising edges and n falling edges. When an odd number of edgesis created, there will be n CE_CLOCK rising edges and n+1 falling edges.The control events are decoded from the thermometer code counter valueas shown in FIG. 11. The decoded control events are used as inputs ofthe logic trees of flip-flops clocked by the falling edge of TCK(C). TheReset Event is also used to inhibit the drive of the TMS(C) pin with aT4-T5 TAP.7 controller.

Control events are detected in this manner by a T0-T2 TAP.7 implementinga Reset and Selection Unit and a T3-T5 TAP.7. The use of the term“minimum period of TCK(C)” means the TCK(C) period when the TAP.7 isoperated at its maximum specified frequency. A control event should bedetected and its associated function performed provided all thefollowing timing constraints are met: 1) the first TMS(C) edgeassociated with a control event follows the rising edge of TCK(C) by aminimum TCK(C) period; 2) TMS(C) edges follows the first TMS(C) edgeassociated with a control event by at least one minimum TCK(C) period;and 3) TCK(C) falling edge follows the last TMS(C) edge associated witha control event by at least one minimum TCK(C) period.

The count of the TMS(C) signaling edges begins at zero immediately afterany of the following: Type-0 reset, Type-1 reset, Type-2 reset, or aTCK(C) signal value of logic 0. The count of the TMS(C) signaling edgesrelated to control event detection is incremented when all of thefollowing are true: Type-0 reset is inactive, Type-1 reset is inactive,Type-2 reset is inactive, the TCK(C) value is a logic 1, and either ofthe following are true: the TMS(C) signal switches from a logic 1 to alogic 0 or the TMS(C) signal switches from a logic 0 to a logic 1.

In some embodiments, a TAP.7 controller detects a control eventindependent of the TMS(C) pin drive history while TCK(C) is a logic 1.

FIG. 12 is a flow diagram illustrating a method for signaling controlevents to a target system having a plurality of components coupled to ascan path. In normal operation, the TCK(C) signal line carries 1202 theclock signal and the TMS(C) signal line carries 1202 the mode data in afour wire interface or the mode and scan data in a two wire interface.The data is generally synchronized to the clock signal. When a controlevent is to be transferred to the target system, the clock signal isheld high 1204 for an extended period of time. While the clock signal isheld high, the data signal is transitioned a number of times to indicatethe desired control event. The target system detects 1206 thiscondition, and counts the number of edge transitions that occur whilethe clock signal is held high. Once the clock signal is released andresumes normal operation, the target system can determine the controlevent based on the number of edges counted, as listed in Table 2.

Other Embodiments

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the invention will beapparent to persons skilled in the art upon reference to thisdescription. For example, edge transitions on the data signal may becounted while the clock signal is held at a low logic level. In anotherembodiment, more than four events may be signaled by defining a largernumber of edge counts. For example, detection of ten or eleven edges mayimply a fifth type of control event, detection of twelve or thirteenedges may imply a sixth type of control event, etc.

In another embodiment, more than two edges may be used for each controlevent. For example, 2-5 edges may represent a first event, 6-11 edgesmay represent a second event, 12-19 edges may represent a third event,etc.

In another embodiment, a device other than a TAP may be configured toreceive data on a data signal synchronized to a clock signal in one modeof operation and to detect an event when the data signal is toggled fora range of counts while the clock signal is held at either a high or alow logic level in a second mode of operation.

In another embodiment, two or more data signals may be toggled to conveytwo or more events simultaneously.

In another embodiment, the data signal may be toggled during a normalperiod of the clock signal, rather than holding the clock signal for anextended period.

Although the embodiments of the invention find particular application tosystems using Digital Signal Processors (DSPs), implemented, forexample, in an Application Specific Integrated Circuit (ASIC), otherembodiment may find application to other types of systems, which mayhave another type of processors. Another embodiment may also be a systemthat does not include a processor. An ASIC that embodies the inventionmay contain one or more megacells which each include custom designedfunctional circuits combined with pre-designed functional circuitsprovided by a design library, wherein some or all of the megacellsinclude a test access port.

An embodiment of the invention may be a substrate to which is attachedmultiple chips that have individual test access ports, commonly referredto as multi-chip modules. An embodiment may include stacked die devicesthat have individual test access ports. Another embodiment may be asubstrate, such as a printed circuit board, to which is attachedmultiple chips that have individual test access ports.

As used herein, the terms “applied,” “connected,” and “connection” meanelectrically connected, including where additional elements may be inthe electrical connection path. “Associated” means a controllingrelationship, such as a memory resource that is controlled by anassociated port. The terms assert, assertion, de-assert, de-assertion,negate and negation are used to avoid confusion when dealing with amixture of active high and active low signals. Assert and assertion areused to indicate that a signal is rendered active, or logically true.De-assert, de-assertion, negate, and negation are used to indicate thata signal is rendered inactive, or logically false.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

1. A method for signaling control events to a target system having aplurality of components coupled in a scan topology, the methodcomprising: receiving a clock signal that transitions between a firstlogic state and a second logic state; receiving a data signal thatcontains data synchronized with the clock signal; detecting two or moreedge transitions on the data signal while the clock signal is held atthe first logic state; counting a number of the two or more edgetransitions on the data signal while the clock signal is held at thefirst logic state; and determining a control event based on the countednumber of edge transitions on the data signal when the clock signaltransitions to the second logic state.
 2. The method of claim 1, whereinfor an integer number n, when 2n or 2n+1 edges are counted, a samecontrol event is determined.
 3. The method of claim 1, wherein for aninteger number r and s, when a number of edges in a range of r to r+sare counted, a same control event is determined
 4. The method of claim1, wherein the edge transitions occur while the clock signal is held foran extended period of time.
 5. The method of claim 1, wherein the edgetransitions occur while the clock signal continues to operate in aconstant periodic manner.
 6. A digital system, comprising: circuitryconfigured to receive data on a data signal synchronized with a clocksignal in a first mode of operation; a counter coupled to the datasignal and to the clock signal, the counter operable to count a numberof edges on the data signal that occur while the clock signal remains ata same logic level; and decoding circuitry coupled to the counter fordecoding one or more events based on a value of the counter.
 7. Thedigital system of claim 6, wherein the decoding circuitry is operable todecode the one or more events, such that for an integer number n, when2n or 2n+1 edges are counted, a same event is decoded.
 8. The digitalsystem of claim 6, wherein the decoding circuitry is operable to decodethe one or more events, such that for an integer number r and s, when anumber of edges in a range of r to r+s are counted, a same event isdecoded.
 9. The digital system of claim 6, wherein a plurality ofcounters and decoders are coupled to a plurality of data lines fordecoding an event on each of the plurality of data lines.
 10. Thedigital system of claim 6, wherein the clock signal is a test clock(TCK) of a test access port, and the data signal is a test mode signal(TMS) of the test access port.